710 



MISS B. LINDSAY ON THE AVIAN STERNUM. [Juue 16, 



separate nuclei for the trochanters of the femur, or the epiphyses of 

 long bones. 



It will be seen that the above conclusions lead us to a much more 

 complete and detailed idea of the nature of the parts of the sternum 

 than at first sight it appeared possible to attain. If the attempt to 

 form a complete theory of the origin of the sternum appears a rash 

 undertaking, in the face of the opinion expressed by Prof. Parker, 

 that our anatomical knowledge of the parts is as yet insufficient for 

 teleclogical interpretation, it must be remembered that the study of 

 five types has afforded a variety of new and interesting facts, and we 

 may at least expect that wider investigation will shortly afifoid a true 



Fis. IV. 



Left figure, tlieoretical diagram of the Ostrich sternum ; right figure, of Rhea ; 



middle figure, of Ohick. 



The costal sternum is left white ; ac, pc, indicate its anterior and jJosterior 

 parts, produced by ribs atrophied in the adult ; the metasternum is 

 shaded vertically, also the anterior-lateral process. Additions of later 

 pliylogenetic date are shaded horizontally. In the Ostrich and Rhea, 

 M, indicates the limit of the ossification in the adult ; o, the dotted 

 spaces, are the centres of ossification in the young ; /, is a fontanel, 

 scarcely closed by thin bone in some specimens. 



solution of the problems under consideration, even if in the present 

 instance the effort to attain it is unsuccessful. 



The theoretical construction of the sternum thus adopted will be 

 best explained by reference to the above diagrammatic representation 

 of the sternum in Fig. IV., and to the following tabular classification 

 of the parts of the Avian sternum. 



That the boundaries of ossification have not always a phylogenetic 

 significance is clearly shown in the Ostrich. Comparison of the 

 embryos (Plate XLII.) shows that the primary costal halves of tbe 

 sternum become united by cartilage developed in the median line, yet 

 the line of ossification is as indicated in the diagram. 



